Multicystic dysplastic kidney (MCDK) occurs as a result of inadequate induction of maturation of the metanephric blastema by the ureteric bud.
The results can be divided into two types. In the first, pelvoinfundibular MCDK, randomly distributed, non-communicating cysts
replace normal renal parenchyma. The kidney is not functional, and an atretic ureter is often present. The second type, hydronephrotic
MCDK, is thought to occur later in gestation, representing a severe, in utero form of UPJ obstruction. There is a dominant cyst in the renal
pelvis region surrounded by intercommunicating, radially-oriented cysts in the typical position of renal calyces. The ipsilateral ureter is
often occluded at the ureteropelvic junction, and minimal renal function is possible. Both forms present with an abdominal mass detected during
infancy, and are associated with contralateral UPJ obstruction. UPJ obstruction with associated hydronephrosis is the most common palpable abdominal
mass in newborns.

Gray scale ultrasound of right kidney in a newborn shows no normal renal parenchyma and the right
renal fossa filled with multiple simple appearing cystic structures c/w MCDK. The cysts did NOT communicate
thereby excluding hydronephrosis. The left kidney showed a congenital UPJ obstruction (Click
here here to see
the contralateral UPJ obstruction. Click the BACK button to return to this page).

(1) Contrast enhanced CT scan of abdomen and (2) coronal and (3) sagittal 3D reconstructions shows multiple cysts (c) of varying sizes (some are calcified) in the left renal fossa in a pattern most consistent with MCDK.